Shock absorber



Oct. 16, 1951 R. H. wHlsLER, JR

SHOCK ABSORBER original Filed Aug. 21, 1950 Z5 Sheets-Sheet l dk 5 AM mii 3 .h E i mw ,l 7 5 UCL 16, 195i R, H, WHELER, 1R Re. ZA k SHOCK ABSORBER 3 Sheets-Sham Original Filed Aug. 21, 1950 Oct 16, 195l R. H. wHlsLER, .1R

SHOCK ABSORBER 5 Shee'LS-Shee 3 Original Filed Aug. 2l, 1950 INVENTOR.

I BY

Reissued ct. 16, 1.1951v SHOCK ABSORBER Ralph H. Whisler, Jr., Monroe, Mich., assigner to Patent Development Company, Monroe, Mich.,

a partnership Original No. 2,546,051, dated March 2.0, 19,51, Se-

rial No. 180,539, August 121, 1950, Application for reissue VMay 24, 1951, Serial No. 228,105

(Cl. 18S-,88)

Matter enclosed in heavy brackets appears inthe original patent but forms no part 4of this reissue specification; matter printed in italics indicates the additions made by reissue.

13 Claims.

This invention relates to shock absorbers of the hydraulic direct-acting type, such as shown in the copending patent application of Brouwer D. McIntyre et al. .for Shock Absorber Construction, Serial No. 171,472, filed June 30, 195-0, now Patent No. 2,546,038, March 20, 1951, and is a continuation in part of applicants copending application, Serial No. 136,949, lfiled January 5, 1950, now abandoned.

The shock absorber illustrated and described in the aforementioned McIntyre et al. copending application is-of the type having a restricted opening in the piston and a restricted opening in the compression base valve at one end of the shock absorber pressure cylinder. The restricted opening in the piston has one end thereof normally closed by means of a valve disk which is actuatable by a predetermined fluid pressure to permit uid to flow from the upper portion of the pressure cylinder to the opposite side of the piston, adjacent the base compression valve. The base compression valve -restricted opening is likewise normally closed by a valve disk which is actuatable to permit iiuid to flow from thefpressure -cylinder to the reserve chamber. Due to this structure, the shock absorber shown inthe copending application is provided with kboth pressure and velocity responsive means for controlling the now of Huid from the pressure cylinder to the reserve chamber and from the upper portion of the pressure cylinder to the lower portion thereof. vThat is, on rebound stroke of the shock absorber, when the piston moves away from the base valve, vfluid will flow through the piston restricted vpassageway and when a predetermined fluid pressure has been built up the valve disk will be actuated to permit the uid to flow to the opposite side of the pressure cylinder. At relatively low velocities very little resistance to the flow of fluid is occasioned by the restricted sizeof the piston opening. However, as the velocity of the piston increases, the opening will provide increasingly higher resistance to the flow of fluid therethrough and in effect forms vvelocity responsive means for controlling the flow of fluid through the piston at high velocities. The same is true of the base valve construction on the compression stroke, that is, upon'movement of the piston toward the base valve assembly.

The advantages of this type of shock absorber are fully set forth in the McIntyre et al. cependlng application. It has, however, been found that even vif the base valve assembly is `provided with pressure and :velocity ,responsivemeans for l,controlling the ilow of fluid from the pressure cylinder to the reserve chamber and thus providing compression control for the shock absorber, the piston is in effect doing substantially no work on the compression stroke, and is therefore provid,- ing practically none of the ,Shock absorber rcompression control. If `the piston is constructed so ,that it will provide a substantial kpart of the shock absorber kcompression control, then the size of the shock absorber, that ris the diameter of the pressure .cylinder bore, ,can be materially lessened, if .the Vdesired rebound .control is not such as prevent it, due to the fact that the rpiston is co,- operating With the base valve ,to provide the nec.- `essary control. As a result a smaller shock ab:- sorber can be used to perform the same amount or work that a larger shock absorber, in which the base `valve alone does all the Work, is capable of doing.

By obtaining as much work as possible ,from the piston and fluid passing therethrough, vinter- .nal operating pressures during the compression stroke .of the shock absorber are reduced and thus the operating life `of the shock absorber is increased vand stroke loss or :lag `due to aeration of .the shock absorber vfluid Vis decreased. Still fur- -ther,r.this type of shockabsorber constructionreduces control losses in the shock absorber due Lto wear kand valve spring set, The obtainance of as much .work as possible from the piston and fluid passing therethrough may be obtained in more than one way. rIt may be obtained by restricting both the piston compression passages as well as `the compressionlpassage or passages inthe base valve and by using in conjunction with thesepas.- sages `pressure responsive means. In this type of construction the pressure Yresponsive means act to provide the primary control during low piston velocities and the restricted passages act to pro,-

vide the vprimary control at high `piston velocities due totheir oriceeffect. lThe resultsof this invention can also be achieved by providing a pis.- ton having restricted compression passages therein, while the `base Avalve passages may be either completely unrestricted or only restricted to a limited extent. In such cases,the pressure responsivevalve-means in the base valve must be balanced or correlated with the piston assembly so that therpiston assembly will not develop internal pressures, at ,any piston velocities developed when the shock absorber is mounted 'on a vehicle or the like, which are Agreater Athan the pressures producedby the base valve assembly at the same piston velocity. Thus, the results of this invention may be` achieved by only festneting the piston passages and by properly balancing or correlating the base valve assembly relative thereto; but, in any event, the piston passages must be restricted in the manner which will be hereinafter set forth, and the base valve must be constructed so as to provide no less resistance to fluid now therethrough than the piston assembly, at any operating velocity, as brought out above.

The applicant, therefore, has devised a shock absorber in whichbetter compression control is obtained than in any shock absorber heretofore known, without at the same time imparting harshness or over-rigidity to the shock absorber action. While shock absorber manufacturers have for years desired to better the compression control of shock absorbers, they have not found `a way to do so without providing either an extremely large shock absorber or one which, when the shock absorber was mounted on an automotive vehicle, or the like, would impart harshness to the vehicle ride. As has been fully pointed outin the aforementioned McIntyre et al. copending application, valve disks or pressure responsive means alone are not sufcient in order to obtain the ultimate in shock absorber ride control for vehicles, and it was found that byusing relatively ilexible valve disks on the piston and base valve assemblies, for controlling the flow of fluid past these assemblies, the ultimate in vehicle ride conditions on rsmooth surfaces such as boulevards could be achieved. Also, by providing restricted openings or velocity responsive means for controlling the flow of fluid past the piston at relatively high piston velocities. such as would be occasioned when a vehicle is traveling over irregular road surfaces, the ultimate in vehicle ride characteristics would be obtained under these conditions, without in any way adversely affecting boulevard ride characteristics. Therefore, by putting the shock absorber piston assembly to work during the compression stroke of the shock absorber, the ultimate in compres- 4Vsion control is obtained, and the size of the shock absorber can be reduced below that which has been heretofore thought possible for performing the same amount of work and providing the necessary control.

It is, therefore, an object of this invention to provide a shock absorber of the aforementioned type, having a variable rate resistance; that is, one in which the resistance for one range of piston velocities can be varied without appreciably aiecting the resistance in the other range of piston velocities.

It is a still further object of this invention to provide a shock absorber of the aforementioned type in which at high piston velocities fluid pressure differential acts on the full area of the piston, less the area of the piston rod, so that a smaller shock absorber than has been-heretofore possible may be produced, which will perform the same amount of work and provide as effective control during the compression stroke as heretofore known larger shock absorbers.

It is a still further object of this invention to provide a shock'absorber of the aforementioned type, which when mounted on a vehicle, will produce the ultimate in vehicle riding conditions both on smooth and irregular road surfaces. Y

It is a still Yfurther object of this invention to provide a shock absorber of the aforementioned type which is relatively simple Iand inexpensive to manufacture, and extremely durable and efficient in use.

These and other objects of this invention willV 4 l become apparent from the following detailed description, taken in conjunction with the accompanying drawings, in which:

Figure l is a longitudinal sectional View of one embodiment of the shock absorber of this invention;

Fig. 2 is an enlarged sectional view of the structure illustrated in Fig. 1, taken along the line 2 2 thereof;

Fig.. 3 is an enlarged sectional view of the structure illustrated in Fig. 1, taken along the line 3 3 thereof;

Fig. 4 is a graphic representation of the resistances provided by a shock absorber of the type illustrated in Fig. 1, at diiferent piston Velocities;

Fig. 5 is a longitudinal sectional view, similar `to Fig. 1, of a further embodiment of this invention;

Fig. 6 is an enlarged sectional view of the structure illustrated in Fig. 5, taken along the line 6 6 thereof;

Fig. 7 is an enlarged sectional view of the structure illustrated in Fig. 5, taken lalong the line I 'I thereof;

Fig. 8 is an enlarged sectional view of the structure Within the circle 8 of Fig. 7

Fig. 9 is a fragmentary longitudinal sectional view similar to Fig. l, of a base valve assembly and adjacent shock absorber parts of a further embodiment of the invention;

Fig. 10 is a sectional view of the structure illustrated in Fig. 9, taken along the line I0 I0 thereof; and n Fig. 1l is a graphic representation of the resistances provided by a shock absorber of the type illustrated in Fig. 9 at different piston velocities.

Referring now to the drawings, and more particularly to Figs. 1-3 inclusive, it will be seen that the shock absorber includestelescoping sections 8 and 9, which are movable longitudinally with respect to each other when the shock absorber is attached between the sprung and unsprung portions of a vehicle, or the like. f The section 8 includes a tubular member Il, having an end cap I3 secured to the upper end thereof. The end cap I3 is adapted to be connected to the sprung portion of a vehicle, by means of ya ringlike attaching element I5. A piston rod I 'I has its upper end rigidly connected to the under side of the base portion of the cap I3 and depends therefrom into the section 9, as will be hereinafterfbrought out. 'I'he section 9 includes a tubular member I9, which is concentric with the tubular member II and partially surrounded thereby. and which forms a fluid reservoir chamber for the shock absorber. A second tubular member 2|, is concentrically disposed within the reserve tube I9, and forms a pressure cylinder within which the main operating parts of the shock absorber are disposed. The lower end of the reserve tube I9 is closed by means of an end cap 23 which is adapted to be connected to the unsprung portion of a vehicle by any suitable means, such as a ringlike attaching member 25. The upper end of the reserve tube I9 is closed by means of an end cap 21 which is provided with n a central aperture 29, in the base portion thereof, through which the piston rod vI'I extends.

The upper end of the pressure cylinder 2| is closed by means of a head or piston rod guide member 3|, which is provided with a reduced portion 33, which flts into the upper end of the pressure cylinder 2|. The rod guide 3l is proand? adjacent the' puter periphery thereof, with a, Vplurality of ci rcinnferentiallyl spaced upwardly egteridingprojections 35, which engage the end c ap 2 1, andwthereby lock the rod guide against mev'ementywith respect to the 4pressure tube 2|, Wirrenl the shock absorber is assembled. The rold guide` 3| is provided with a central aperture 31, throughWhich the piston rod I1 extends. A rubber seal 39 surrounds the Apiston rod I1 and is c oni`ined withinnthe upper portion of theend cap v2'] by means of a retainer element 4| and a spring l43, the lowerrnost convolution of which seats, upon the u pper face of the rod guide 3`I, within the confines of the projections 35.

, j lfhe lower end of the pressure cylinder 2| is closed by means of a base compression valve assembly` having a valve body 45. The cylinder end or valve body 45 is providedron the outer periphery thereof with a reduced portion 41, over which the lowerrend of theI pressure tube 2| is fitted. The bottom face of the valve b'o'dyf45 abutsdthe end cap 21|, so that the valve body is l o c ked against movement between the end cap and the pressure tube 2|.n The valve body `45 is proyided adjacent the lower end thereof withva plurality of circumferentially spaced passageways 49, which communicate the reserve chambei' I9 with the under side of the central portion ofthe valve body 45.

vThe reserve tubeor chamber I9 is adapted to contain a reserve supply of hydraulic medium, in addition to that which is disposed in the pressure cylinder 2|, and the fluid in the p-ressure cylinder is displaced in dependence upon relative movement of the shock absorber sections 8 and 9 bynieans of a piston 5I, which is connected to the lower end of the piston rod I1 for reciproca- `within the pressure cylinder upon relative movement of the shock absorber sections. The lower end of the piston rod I1 is reduced in diameteruat 53 to extend through the piston 5|. A support washer 55, having an annular ilange 51 en the upper end thereof, abuts the shoulder formed at the upper end of the reduced piston rod portion 53, and has its lower end disposed in a recess in the upper face of the piston 5I, adjacent the piston rod reduced portion 53. n The piston 5I is provided with an outer set o f circumferentially spaced, restricted passageways ,59 and a pair of opposed restricted passageways A5I, which are disposed radially inwardly from the puter set of passageways 59. Three passageway's 59 are illustrated as comprising the outer set of passageways for the piston, for reasons which will hereinafter appear. piston` 5| is provided with a circumferential upwardly projecting rim or land 53 between the inner and outer sets of passageways 59 and 6|. A second upwardly projecting land or rim4 65 is provided on the upper surface of the 'piston 5| adjacent the outer periphery thereof. A disk type valve 61 is seated upon the upper faces of annular lands E3 and 65 and is of the type illustrated in Fig. 3. The valve 61 closes off the upper ends of the outer set of passageways 59 and is provided with openings 69 above the inner set of passageways 6|, so as not to affect the flow of lluid through these passageways. The disk valve 61 is resiliently held in engagement with the .lllpperiace of the piston 5| by means of a star shaped spring 1I. The spring 1I is slidably supported on the shank portion of the support 4washer 55, and the annular flange of the support washer engages the inner peripheral portion of the star spring so as to preload thedlsk valve B1 The upper face of the through the spring 1I, al predetermined amount'. The disk valve 61 thus lies flat on the piston lands 63 and 65 and is not clamped against the lands but rather is free to be lifted off of its seat against theaction of the spring 1I.

l,',Ihe `piston 5| is locked on the reduced piston rod portion 53, with its upper face engaging the lower face of the support washer 55, by means of anut 13, which is threaded on the lower end of the piston rod reduced portion 53. The bottoni face of the piston 5I is provided, in addition to a.V downwardly projecting land 15, which corresponds to the land 53 previously described, with e; downwardly projecting land 11, adjacent the piston rod reduced portion 53. A laminated disk valve 19 abuts the bottom faces of lands 15 and 11, so as to normally close on the lower end of th two inner passageways 6|, and the nut 13 engages the bottom face of the disk valve 19 so as to resiliently maintain the disk valve in position te normally close off the lower ends of the two piston openings GI.

The compression base valve body 45 is provided with an outer set of circumferentially 'spaced passageways 89 and a single inner passageway 9|. While more than one passageway 9| may be provided, if desired, the shock absorber illus'- trated in Figs. l-3 is provided with only one passageway, so that a ratio of three to one between the piston passageways 59 and the base valve passageway 9| is provided. That is to say, the total flow capacity of the three piston passageways 59 is three times as great as the flow capacity of the valve passageway 9|. The three to one ratio is arrived at from the fact that the area of the rebound chamber i. e. the area of the pressure cylinder bore less the area of the operating rod |1, is substantially three times the area of the operating rod, so that when the piston 5I moves toward the base valve 45 during the shock absorber compression stroke, as will hereinafter more fully appear, three times as much fluid will now up through the piston passageways 59 as through the base valve passageway 9|, so as to continually maintain the upper portion of the pressure cylinder, between the rod guide 33 and the piston 5|, completely filled with fluid at all times, thus preventing, or at least materially reducing any gas or air pockets or vapor from being formed in the upper portion of the pressure cylinder, which would adversely aiect the operation of the shock absorber. At the same time the piston passageways 59 and 6| are of a relatively small size, so as to provide resistance to the flow of fluid therethrough at high piston velocities, as will more fully hereinafter appear.

The upper and lower faces of the valve body 45 are provided with lands in the same manner as the upper and lower faces of the piston, so that the lands thereof are indicated by primed numbers corresponding to like numbers in the piston construction. IThe base valve body i5 is provided with a central aperture 9S, through which is extended the shank portion of a partially hollow rivet 96. The lower end of the valve body passageway 9| is normally closed by means of a laminated disk valve 91 which has the outer periphery seated against the bottom face o1 the land 15 and the inner periphery held in engagement with the lower face of the valve body by a spun over portion 99 on the lower end of the rivet shank 95. The outer periphery of the laminated disk valves 91 can thus be unseated or moved away from the lower end of the valve body passageway 9| by a predetermined fluid pressure.

The upper ends of the base valve passageways 89 are resiliently closed by means of a disk valve IUI which corresponds to the disk valve 61 used in the piston construction. A star spring |03 holds the disk valve |i in its closed position, in the same manner as previously described in con- `iunction with the piston. The rivet 96 is formed with an annular flange or head |05 in the upper end thereof, which engages the star spring ID3 so as to load the disk valve IllI by a predetermined amount in the same manner as previously described.

It should at this time be pointed out that the two inner passageways 6I in the piston 5I, and

the single inner passageway 9| in the base valve body 45, are of such a size as to offer only a minimum of resistance to the ilow of fluid therethrough when the shock absorber is being actuated at a relatively low velocity suoli as 385 inches per minute or less, but will offer increasingly higher resistance to the flow of fluid therethrough after the valve disks 'E9 and 97 have been opened, as the cycle of operation of the shock absorber increases, as will clearly appear hereinafter.

In operation, when the piston 5i travels downwardly the fluid in the pressure cylinder 2 I, below the piston 5|, passes upwardly through the outer piston passageways 59 and the pressure of the fluid moves the disk valve 61 ofi" its seat on the lands 63 and 65 against the action of the star spring 1I` and enables fluid to flow into the upper portion of the cylinder above the piston. Due to the fact that the piston rod I1 occupies a portion of the cylinder 2| above the piston, the available space in this portion of the cylinder is less in volume than the space below the piston. Thus, as the piston continues to move downwardly fluid will be displaced by the rod through the opening 9| in the base valve and will flow into the reserve chamber I9. In order to prevent cavitation in the shock absorber, it is extremely important that the upper portion of the` pressure cylinder, above the piston, be lled with fluid at all times, so that gas or air pockets or voids will not form. As the ratio between the area of the cylinder bore less the area of the operating rod, and the area of the rod I1 is approximately three to one in the shock absorber illustrated, three passageways 59 are provided in the piston as compared with one passageway 9| in the base valve so that the total l area of the three passageways 59 is three times the area of the passageway 9|. Therefore, a greater volume of fluid will flow upwardly through the passages 59 to the upper portion of the pressure cylinder so as to maintain the same in a filled condition, The resistance to the flow of fluid offered by the piston valve disk 69 and star spring 1I is less than the resistance offered by the base valve laminated disk 91, so that the uid will flow upwardly through the piston before it flows downwardly through the base valve opening 9 I. As the piston continues to move downwardly sufficient pressure is built up against the disk valve 91 of the base valve assembly to unseat or move the latter oil its seat on the land and to permit the displaced fluid to flow into the reserve chamber I9 through the opening 9|. However, as will hereinafter appear, if the piston is operating at high velocities, resistance to the flow of fluid through the passages 59 and 9| will be set up by the passages themselves for controlling the flow of fluid to the upper portion of the cylinder and to the reserve chamber, in addition to the control provided by the valve disks.

When the piston 5I moves in an upward direction in the pressure cylinder 2|, the fluid under pressure passes through the two piston passage- Ways 6I and acts against the laminated disk valve 19 to force the same off its seat on the land 15, and permits the fluid to flow from the upper portion of the cylinder into the portion of the cylinder below the piston. As the piston 5| travels upwardly in the cylinder, the piston rod I1 moves out of the cylinder and, therefore, it is necessary to replenish the lower portion of the cylinder with the fluid. This additional supply of fluid is supplied from the reserve tube I9, through the base valve passageways 89, which fluid unseats the disk valve |0| against the action of the star spring |03, which opens relatively freely so that very little or no resistance is offered to the flow of fluid from the reserve tube, thus replenishing the supply of fluid in the lower portion of the cylinder. Again, it must be pointed out that the fluid flowing from the upper portion of the cylinder through the two piston passageways 6I will be controlled primarily by the pressure responsive disk valve 11, during low piston and fluid velocities, and by the disk valve 11 and the additional resistance set up in the passageways 6| themselves when the shock absorber is operating at high piston and fluid velocities.

Referring now to Fig. 4, wherein a graphic resistance curve is shown for the shock absorber of this invention, it will be seen that when the piston is moving upwardly at a velocity of approximately 385 inches per minute, the piston resistance to fluid flow from the upper side to the lower side thereof is approximately pounds. When the piston velocity increases to 1100 inches per minute, the resistance is increased to pounds. When the piston velocity is increased to 2300 inches per minute the piston resistance increases to 310 pounds, and when the piston velocity reaches approximately 3900 inches per minute the piston resistance is increased to 615 pounds. With the construction of this invention, due to the use of valve disks, resistance is still obtained in boulevard riding, as

indicated by the generally straight line nose of each curve, and the necessary resistance for pro-per control during rough riding is obtained by the use of the restricted passageways. When the piston moves downwardly at a velocity of approximately 385 inches per minute, the total resistance offered by the base compression valve and the piston is approximately 50 pounds. When the piston velocity increases to 1100 inches per minute the total resistance is increased to 82 pounds, and when the piston velocity reaches 2300 inches per minute the total compression resistance is increased to 153 pounds. When the piston velocity reaches 3900 inches per minute the total compression resistance is increased to 2'18 pounds. Of course, as the velocity continues to increase the resistance will greatly increase, and on washboard roads the piston velocity may reach 6000 inches per minute` It will thus be seen that with the construction of this invention, wherein restricted passageways 6I and 59 are provided in the piston for controlling rebound and compression strokes, respectively, and a restricted passageway 9| is provided in the base compression valve for cooperating with the piston compression passageways 59, the resistance to the flow of fluid through the piston and base valve at high piston velocities is a great deal higher than that obtained with a conventional type of shock absorber wherein orifice resistance is removed as much as possible. Also, it will be absorber oi' this invention, it has been foundY that at low velocities of around 385 inches per minute there was practically noicompression control caused by the piston, and that the compression control was primarily 4achieved through the base valve structure. When the piston velocity was increased to 1100 inches vper minute, vonly 16% of the total compression control was caused by the piston. However, :as the velocity of the piston increases, the 'percentage of the total compression contro-l contributed by the piston likewise increases, so thatat 2300 inches .per `minute the piston provides `35% of 'the compression control, and at 3900 inches per iminute itprovides 48% of the total compression control. .It will .thus be appreciated that the restricted passageways 59 in the piston provide a .substantial portion of the compression control of the shock absorber and cooperate with the base valve to .provide mo-re efficient control and to enable the use of a smaller shock absorber from which the same amount of work may be achieved as from heretofore known conventional rshock absorbers.

Thus, while a relatively `light disk valve 61 is used on the compression side ofthe piston, so as not to impart .any harshness to'the vehicle ride on .relatively smooth pavement, the restricted passageways'59 provide the necessary control at high piston velocities to give the ultimate in vehicle ride characteristics on irregular road surfaces on "the compression stroke of the piston. It will, of course, be understood that the ratio of three to one between the piston passageways 59 and base valve passageway 9| may be varied in accord- `ance with variations in the ratio between the area of any given 4pressure cylinder less the area of the operating rod, and the area of the rod, and .it will also be understood that the three to one Iratio is only a minimum to insure proper filling of .the pressure cylinder, and that more openings may be provided in the piston if less compression resistance is desired, as heretofore described. In any case, the sizeof the base valve passageway .9| can be readily selected to maintain such three to one ratio after the size and number of piston passageways 59 fora given shock absorber has been determined. It will furthermore be understood that the aforementioned three toA one ratio applies only where the vlength .or depth of the piston and base valve bodies are substantially the same, but the ratio may not apply if, for example, the piston were relatively thin and the base valverelatively heavy. In other words, the ,primary importance resides in the fact that the ratio between the sizes-f the holes in the base valve and piston assembly, i. e. the length and diameter, must be such that three times as much fluid can iiow through the piston than through the kbase valve where the area of the pressure .chamber less the area of the operating rod and .the area `of the rod are in a three to one ratio. In .certain instances this ratio may be decreased if the base valve `disks are properly correlated with .the piston assembly, as will hereinafter appear.

.In ythe cbtainance oi the aforementioned results rshown in Fig. 4, three -.0? diameter holes or `openings .50 were ,provided which Were approxi- The `disk 61 was .015" thick and the spring steel star spring 'H was .012" thick. The maximum resistance offered by the disk and spring at a piston velocity of 3900 per minute was only about ltten pounds. Three .020" thick, disks 15' were-used to close the lower end of the base valve opening or passage 9| and the lower end of the rivet 9G was spun to a pressure of 300 pounds against the inner periphery of the disks 'l5'. While the passages or openings were of the aforementioned sizes these passages will only provide the results illustrated in Fig. 4 with a fluid or liquid of a certain viscosity and Where the diameter of the pressure cylinder is one inch and the diameter of the operating rod I'l is one-half inch. The liquid used in the test from which the results illustrated in Fig. 4 were obtained had La viscosity of -90 Saybolt seconds at 100 F. V(3f cours-e, the hole diameters could be altered to'vary the resistance curve when a liquid having the stated viscosity was employed and could be altered to obtain the same resistance if a fluid or liquid of .a different viscosity were employed'in the Shock absorber. Likewise, these diameters may vary as the length of the passages is varied, so vlong as the same resistance to fluid flow `is maintained thereby. Furthermore, for different size pressure cylinders the passage sizes would have to be changed in order to obtain thesame resistance values as will be seen from the table hereinafter set forth.

Thus it will be appreciated that while the results shown in Fig. 4 were obtained with passages of the sizes heretofore mentioned, they could be obtained with various other passage sizes. Also, it should be distinctly understood that the results shown in Fig. 4 could be varied by varying the characteristics o the valve disks which close the passages. Still further, the curve illustrated in Fig. 4 and the resistance desired from the shock absorber will vary with different types of vehicle suspension systems on which the shock absorber is used, and with various types and Weights .of vehicles on which the shock absorber is mounted. The sizes of the piston and base valve passages and the Aresistance obtained are merely illustrative of one specic example of a shock absorber of this invention and are not to be considered as limiting the invention to the example illustrated.

From tests that have been run it is indicated there is a critical relationship for predetermined passage length, between the area of the piston compression passages 59 and the .area of the ypressure cylinder less the area of the operating rod, i. e., the rebound chamber of the Apressure cylinder. For example, ina shock absorber `having a one .inch bore or pressure cylinder the area of the pressure cylinder is .7854 square inch, and if -a one-half .inch diameter operating rod is used the .areaof the operating rod is .196 Square inch, so that the area of the rebound chamber Lis the difference, or..589 square inch. The piston has three compression passages each .076 in diameter., and each having anarea of .00455 square inch. Thearea of `the three holes is, therefore, .three times .00455 square inch,.or .0.1365 square inch, which .when divided .by .589 square inchis Vrod area, the following table is presented. This these exact sizes.

approximately 2.3% of the area of the rebound chamber. Tests indicate that if the total crosssectional area of the piston compression passages, for this size shock absorber, where the length of 12 Furthermore, the length of the passages for the different sized shock absorbers was in the vicinity of 1%" and did not vary enough to effect the data presented.

t P. t 0 T al llercentae of pera xs on petot assage rea (1J) rislsllg ing Rod Passage Num (1; rrsll, ating Piston Relative to Diameter Diam- Diamber of rea Rod Passage Y Rebound Y eter eter Piston Area Area Chamber 1 Area Passages PA O D P CA DA PA C A-DA Inches Inches 7/ 'Ms .048 1 .6013 1503 .0018 .4 725 'Ma 076 5 6013 1503 0225 5 1 M 055 1 7854 196 0023 4 1 l 079 6 7854 196 02945 5 1 B 076 3 7854 196 01365 2. 3 1% 9s 0775 1 1. 485 307 0047 4 1% 5/ 112 6 l. 485 307 0589 5 2 1 109 1 3. 1416 7854 0094 4 2 1 158 6 3. 1416 7854 1178 5 the passages is approximately g of an inch, is less than .0024 square inch or .4% of the area of the rebound chamber, the results of this invention cannot be satisfactorily achieved because relatively free ow of iluid at low velocities is no longer present. Likewise, it appears that if the total cross-sectional area of the piston compression passages exceeds .020 square inch, or 5%. of the area of the rebound chamber, the results of this invention will not be properly achieved because the desired orice effect at high velocities is not obtained. Thus it appears that the area of a piston compression passage or passages should be between .4% and 5% of the area of the shock absorber rebound chamber. Of course, if the length of the passages were increased materially, the diameter of the passages could likewise be increased and the same resistance values obtained. Such increases are considered to be within the scope of this invention when the same general type of results are achieved. The same is true when a liquid of a dilerent viscosity from that mentioned above is used. It Will thus be seen that there is a critical relationship between the area of the piston compression passages relative to the area of the shock absorber rebound chamber, if the length of the passages does not vary and if fluid of a generally normal and conventional viscosity is employed.

In order to show the relationship between the area of the piston passages and the shock absorber size, rebound chamber area, and operating table denotes piston passage sizes which are illustrative only, but the area of which is determined to produce a given percentage of area relative to the shock absorber rebound chamber area, in accordance with the critical range referred to above. This table furthermore presents the aforementioned data only for 1", 1% andy 2l pressure cylinder diameter shock absorbers, and of course, the invention is. not limited to Therefore, this table presents the data for the various sized shock absorbers to indicate the relationship between the various areas to obtain the percentage of .4 and the percentage of 5% between the piston passages and the rebound chamber areas., and in addition, for a one inch shock absorber, to show this relationship for the shock absorber from which the results shown in Fig. 4 were obtained, and in Which the area of the piston compression passages was 2.3% of the area of the rebound chamber.

'I'he shock absorber illustrated in Figures 5 through 8 is substantially the same as the shock absorber previously described, with the exception of the compression passageway construction in the piston, and therefore like parts of this embodiment are designated by prime nurnbers corresponding to like part numbers of the previous embodiment. In the embodiment illustrated in Figs. 5 through 8, the outer set of piston compression passageways are formed by means of circumferentially spaced notches or recesses |09 around the outer periphery of the piston body 5|. The depth of the notches or recesses |69 is relatively small and is in the neighborhood of only a few thousandths, so that the total area provided by these recesses is at least three times as great as the area of the base valve compression passageway 9|', in the same manner as previously described for passageways 59. The recesses |99 are separated by means of lands or peripheral portions which engage the inner wall of the pressure cylinder 2|, so as to maintain the piston in sliding contact with the inner wall and in a proper centered relationship with respect thereto. 'I'he upper ends of the recesses or passageways |09 are normally closed by means of an annular lip |3 of a. rubber gasket or rim 5. The lip ||3 normally enga-ges the inner Wall of the pressure cylinder 2| so as to prevent the ilow of fluid from the upper portion of the pressure cylinder to the lower portion thereof. The rim ||5 is held in engagement with the upper surface of the piston body 5|' by means of a washerlike member which is disposed between the shoulder at the upper end of the piston rod reduced ,portion 53 and the upper surface of the piston body 53'. The washer ||1 is ported at ||9 so as not to interfere with the flow of fluid downwardly through the piston rebound passageways 6|. Thus, on the compression stroke of the shock absorber uid ilows upwardly through the recesses |09, and moves the lip ||3 of the rubber rim or gasket ||5 away from the inner wall of the pressure cylinder to permit the flow of fluid to the upper portion of the pressure cylinder.

The recesses |09 are so correlated with respectV and produces the same effect :as the shock absorber previously described.

In the embodiment of the invention illustrated in Figs. 9 through 1l the shock absorber illustrated is identical to Vthe one previously vdescribed, in connection with Figs. `l to 3, except for the base valve, Vso that only the base valve and adjacent portions of the shock absorber are illustrated.` In this embodiment the base valve is provided with three .089" diameter passages 9|" and the passages are, therefore, substantially unrestricted so that little or no orifice control will be obtained from these lpassages even at -high piston velocities. Three disks are provided for closing the passages 9|", each of which is .020" in thickness and all of which are made of spring steel. In the particular shock absorber from which the results shown in Fig. 11 were obtained, the lower end of the rivet 96 was sp-un to a pressure of 375 pounds against the inner periphery of the disks. The piston was constructed in the same manner as previously described and had three .076 diameter compression passages so that a further description of the same will not .be necessary.

Referring now to Fig. l1 it will be seen that with the shock absorber illustrated in Figs. 9 through 11 the piston assembly and base valve q assembly together Will offer a total of fty pounds resistance `to movement of the piston 'toward the base valve at a piston velocity of 385 inches per minute. At a velocity of 1100 inches per minute the resistance offered by the base valve assembly `and the piston assembly together increased to ninety pounds, and at a velocity of 2300 inches per minute the total resistance increased to one hundred and seventy pounds. Further, at the high velocity of 3900 inches per minute the resistance increased to three hundred pounds. Therefore, it will be appreciated that even where the base valve passages are unrestricted, relatively high resistance will be obtained at high lpiston velocities and relatively low resistance at low piston velocities. This results from the fact that the piston compression passages are still restricted. It should be understood that even if both the piston and base valve compression passages were restricted, as described beforel the piston passages would provide 75% of the total orifice control, so that even if 'the base valve compression passage is not restricted, or does not provide orifice control, `the piston passages will still provide substantial orifice control to .produce the `results illustrated and desired within the scope of this invention. It should, however, be pointed out that the base valve disks 75" must be constructed and/or preloaded such that the piston assembly will not develop internal shook absorber pressures at any piston velocities which are greater than the pressures produced by the base valve at the same speed. In other words, the resistance `to fluid flow provided by the base valve disks must always be {edual'to or greater than] at least as great as the resistance to fluid now pro-vided by the piston passages and disks normally closing the same, together, 'in order to provide a shock absorber which will operate properisr and so that `the upper portion of lthe pressure cylinder, between the piston and operating rod guide, will fill and the shock absorber will not starve on the rebound stroke. The results shown in Fig. 1l are, of course, merely illustrative and will vary with iiuids ot different viscosities, different passage sizes, etc. Also, for different types of vehicle suspensions, .control and vehicle weights, .different results `would :be desired and obta'ined, but in al1 cases the base valve disks must be loaded in such a manner that they will provide as great or greater resistance to fluid iiow than does the piston assembly. Furthermore, the piston compression passages 55.9 are still restricted and must be of a size between .4% and 5% of the pressure cylinder rebound area, or the area-,0f the pressure cylinder less the yarea of the operating rod. With the use of a restricted piston excessively high internal pressures are avoided, so that aeration of the liquid will be Areduced to .a Yminimum .and loss of resistance during operation vdue to `piston wear and valve spring s et is effectively minimized.

'Thus the results of this Vinvention may |be pb.. tai-ned e'ither'with .a `piston having restricted compression passages and a base valve having restricted passages and Apressure vresponsive valve disks, or with a restricted piston and a nonre- .stricted :base valve having pressure responsive valve disks which will produce internal `Worlsling pressures as high or higher than those produced .by the piston assembly rat any piston velocity during YShock .absorber operation. In some installations it vhas been found desirable to employ va shock absorber in which the base valve passage is unrestricted, even Ythough all of the orifice -or velocity responsive control must be provided by the piston passages which, of course, reduces vthe efficiency of the velocity responsive controla cer.- tain amount as compared with the construction previously described, vin which the passages of both vthe piston and ybase valve were restricted.

Thus it can be understood that Eif both the piston and base valve compression passages lare restricted, the ratio vbetween the sizes thereof is preferably in substantially `'the same proportion :as the pressure cylinder area fminus the rod area is to the I.operating irod area. This :ratio can, however, be more or .less than that proportion, 4but Vif the 'ratio is increased, or more than 'the proportion, the Veiiciency .of 'the :piston restriction Ior Yorifice control will decrease in .substantially 'the same proportion, and if the i-ratio is decreased, or less than the proportion, the pressure `responsive valve :means or disks of the base valve must `be adjusted. in such a manner that the pressures produced by the basevalve disks and any restric- -ti'on inthe base valve passage will alway be [equal Vto Vor :greater than] at least .aslgret Ais the pressures vproduced by the piston compression Apas- .sage and disk ait all piston velocities during ythe Shock absorber operation. Therefore, Yagain it must :be emphasized `thatthe results of .this invention can be obtained with different balanced .conditions .of 'the pressure responsive and velocity1 responsive means in the shock Vabsorber piston and ebase valve assemblies.

It has been found from actual road tests that when a vehicle is travelling on relatively smooth .pavementthe velocity of the piston will vary from Yabout zero inches :per minute up to .around '500 or 600 inches per minute, while when a vehicle is driven .on rough, irregular surfaces the velocity vof the piston `may reach 6,000 inches `per minute, due primarily to the fact that on rough surfaces the length of the stroke of the piston is greatly increased and the piston may Vmove at wheel frequency rather than at body frequency, -the formerof which is almost ten times the latcter. However, for the purpose .of this disclosure, the following values have been chosen as representing low and high velocity: Low velocity i385 inches :per minute .and high velocity "23.00 .inches l pressure.

15 f per minute or more. It will, therefore, be see that with a shock absorber of this invention the valve disks or pressure responsive means will primarily control the ilow [or] of uid through the piston and base valve when the vehicle is travelling on relatively smooth pavement, a1- though a very small amount of resistance to the flow of fluid, even at relatively low velocities, is set up by the restricted passageways in the piston and base valve and by friction in the shock absorber. However, when the vehicle is travelling over irregular surfaces or rough roads, -the resistance to the ow of fluid through the base valve and piston, or the piston alone, as the case may be, will be controlled both by the restricted passageways and the valve disks, and the majority of this resistance or control is provided by the restricted passageways. Furthermore, with the construction of this invention, the damping rate of the piston and base valve can be easily varied. That is, the resistance at relatively high piston velocities can be varied without materially affecting the resistance to fluid flow at relatively low velocities, and vice versa.

In order to increase the efliciency of the shock absorber on the compression stroke and consequently the unit as a whole, and. permit the use of a shock absorber having a smaller pressure cylinder diameter, applicant has in Yeffect put the piston to work during its compression stroke. In previous constructions, in order to insure proper lling of fluid above the piston during the compression stroke, exceedingly large passageways through the piston have been provided re` piston rod area, and thereby greatly increasesr the resistance of the shock absorber. The original pressure below the piston acts upon the piston rod area in the conventional manner, thus giving a substantial resistance increase directlyr attributable to the size controls placed upon the piston passageways. Since it is important that the chamber above the piston be loaded with fluid at all times so that the rebound stroke will occur normally with a minimum of lag, the pressure above the piston during the compression stroke must be something higher than atmospheric The piston and base valve are directly dependent upon each other in order to produce this relationship during the compression stroke. The total restriction provided by the piston must be substantially the same or less than the total resistance provided by the base valve assembly at all piston velocities which may occur on the vehicle. At any particular piston velocity or any particular pressure, if a volume of fluid equal to that of the piston rod flows through the base valve, a volume of fluid equal to or slightly greater than the volume encompassed by the same given length of the pressure cylinder, less the volume of the piston rod, must ow through the piston. It can be seen that by properly correlating the piston and base valve passageways and pressure responsive disks,

16 this condition can be maintained at all speeds and more work done on the compression stroke of the shock absorbers.

It is therefore possible, with the construction of this invention, to obtain results which have not been heretofore obtained in shock absorber constructions and to provide a shock absorber in which the eiciency and control factors are materially increased without increasing the manufacturing cost, as well as a shock absorber in which the control factors may be easily varied to produce any desired control characteristics in accordance with the type of vehicle or other apparatus on which the shock absorber is mounted.Y

What is claimed is:

1. A hydraulic shock absorber including a pressure cylinder and a reserve chamber, both of which normally contain hydraulic fluid, means closing the opposite ends of said pressure cylinder, including a compression base valve body adjacent one end thereof, a piston slidably disposed in said pressure cylinder, and operating rod connected with said piston and extending through the closure means at the opposite end of said pressure cylinder from said compression base valve body, said piston having a passageway therethrough through which fluid may flow from the compression base valve side of said piston to the opposite side thereof during the compression stroke of said piston or movement thereof toward said base valve body, said piston having another passageway therethrough through which fluid may flow from the operating rod side of said piston to the opposite side thereof during the rebound stroke of said piston or movement thereof away from said base Valve body, valve means normally closing each of said piston passageways and actuatable by a predetermined fluid pressure acting thereagainst to permit a flow of fluid from one side of said piston to the other side thereof, said base valve body having a compression passageway therethrough through which fluid displaced by said operating rod may now from said pressure cylinder to said reserve chamber during the compression stroke of said piston, valve means normally closing said base valve body passageway against the flow of fluid therethrough and actuatable by a predetermined fluid presvsure to permit fluid to ilow through said passageway; said piston compression passageway valve means being actuatable by a lesser fluid pressure than said compression base valve body valve means, means permitting fluid to flow past said base valve body from said reserve chamber to said pressure cylinder on the rebound stroke of said piston so as to replenish said pressure cylinder, the sizes of the piston compression passageway and the base valve compression passageway being of a ratio substantially equal to the ratio between the pressure cylinder area less the operating rod area and the operating rod area, whereby when said piston moves toward said base valve body the necessary volume of iluid will flow through said piston compression passageway to keep the portion of the pressure cyinder on the operating rod side of saidpiston continually lled with iiuid, and said passageways also being of such a size that at relatively low piston velocities the valve means of said compression valve body passageway and said piston compression passageway will primarily control flow of uid through said piston and valve body and at relatively high piston vel, locities said compression Valve body passageway and said piston compression passageway will pro- 17 vide the majority .of .control to the flow of fluid through said piston and valve body.

2,. A hydraulic shock absorber including a pres- .snre .cylinder and a reserve chamber, both of which normally contain hydraulic fluid, means closing the opposite ends of said pressure cylnder including a compression base valve body adjacent one end thereof, va piston slidably disposed in .sa-id pressure cylinder, an operating rod connected with. said piston and` extending through the closure means at the opposite end of said pressure cylinder from said compression base valve body, said piston having a passageway therethrough. through which uid may now from the compression base valve side of said piston to the opposite side thereof during the compression stroke of said piston assembly or movement thereof toward said base valve assembly, means permitting a flow of fluid past said piston from the operating rod side of said piston to the .opposite sid thereof during. the rebound stroke of said piston or movement thereof away fromsaid base valve body, valve. means normally closing said piston compression passageway and actuatable by a predetermined fluid pressure acting thereagainst topermit ,a flow .of fluidfrom .the .one side of said piston to the other .side thereof, said base valve body having a compression .passageway therethrough through which fluid displaced by said operating rod may flow from said .pressure cylinder to said reserve .chamber during .the compression stroke of said piston, valve means normally 4closing said base valve body passageway against the yiiow of fluid ,therethrough and actuatable by a predetermined iiuid pressure to permit fluid to flow through said passageway, said piston .compression passageway valve means being actuatable by a lesser fluid pressure than said compression base valve body valve means, means permitting fluid to flow past said base valve body from saidv reserve chamber to. said pressure cylinder on the rebound stroke of said .piston so as to. replenish said pressure cylinder, the sizes of the piston .compression passageway and .the base valve compression passageway being `of a ratio vsubstantially .equal to the ratio between .the pressure cylinder area less the operating rod area and the operating rod area, whereby when lsaid piston moves toward said base valve body the, necessary volume of fluid will flow through said piston compression passageway tokeep the portion 4of -the pressure cylinder on the .operating rod `side of said. piston vcontinually filled with. fluid, .and said passageways also being of such a size that at relatively low piston velocities the, valve meansf of .said compression valve body 1 passageway andsaid piston compression passageway Will primarily control flow .of fluid through .said piston and valve body and at relatively high piston velocities said compression valve body passageway and said piston corn-pression passageway will provide the majority of control to the -flow of. uid through said piston and valve body.

3. A hydraulic shock absorber including a pressure cylinder and a reserve chamber, bothy of which normally contain hydraulic Iduid, means. closing the opposite-ends of said pressure cylinder including a -base compression valve body adjacent one -end of said pressure cylinder, a piston slidably disposed in said pressure cylinder, an ope-rating -rod connected with saidpiston and extend-ingY through the closure means at the opposite end of s-aid pressure cylinder from said compression valve` body, passageway means in -saidf piston for vpern'litting -a flowv of fluid from the compression valve-body-side of said pressure cylinder to the opposite side thereof during the compression stroke `of said piston or movement thereof toward said base compression valve body. the area of ,said piston passage means being not less than 4% nor more than 5% of the area of the pressure cylinder less the area of said operating rod, means permitting a flow of iluid past said piston from the operating rod side of said piston to the opposite side of said pressure cylinder during the rebound stroke of said piston or movement thereof away from said base compression Valve body, fluid passageway means in said base compression valve body permitting a flow of fluid vdisplaced by said operating rod from said pressure cylinder to said reserve chamber during the compression stroke of said piston, means permitting a flow of fluid past said compression valve body from said reserve chamber to said pressure cylinder during the rebound stroke of said piston, the sizes of the piston compression passageway means and the base valve compression passageway means being of a ratio substantially vequal to the ratio between the pressure cylinder area less the operating rod area and the operating rod area, whereby when said piston moves toward said compression valve body the necessary volume of fluid will flow through said piston .compression passageway means so` as to insure that the operating rod side of said pressure cylinder Will be .continually filled with iuid at all times, said .compression passageway means of said piston and valve body also being of such a size as topermit a relatively free ow of fluid past the piston. and valve body at relatively low piston velocities, and increasingly higher restriction to the ow of fluid from one side to the other .of said piston and valve body at relatively high piston .and fluid velocities, and said piston compression passageway means being such that at relatively high piston velocities the uid pressure differential, between opposite sides of saidpiston, acts upon .substantially the full area of said piston, less the area of said operating rod.

4. I-n a hydraulic shock absorber, a pressure cylinder and a reserve chamber, both of which normally contain hydraulic fluid, means closing theopposite ends of said pressure cylinder including a valve body adjacent one end thereof, a piston .operable in said cylinder and adapted upon movement in said cylinder toward said valve body toipass fluid from the side of the pressure cylinder adjacent said valve body to the other sideof said piston, an operating rod con- -nected vwith said piston and extending through then closure means at the opposite end of said pressure cylinder from said valve body, pressure responsive means for controlling the flow of fluid from the-one side of said piston to the other side, means responsive to the velocity of said piston in said .cylinder `for controlling the flow of fluid from the one side of said piston to the other side in accordance with the velocity of said piston, said valve body being adapted upon said movement of said piston to pass fluid from said pressure cylinder to said reserve chamber, pressure responsive means for controlling the flow of uid fromfsaid pressure cylinder to said reserve chamber, means responsive to the velocity of said piston in said cylinder for controlling the flow of fluid from said pressure cylinder to said reserve chamber in accordance with the velocity of the piston, saidv piston pressure and velocity responsive means and said valve body pressure and velocity responsive means being so constructed thatthe ratio between the flow of fluid past said piston from the said one side thereof to the other `side thereof and the flow of fluid past the valve body from said pressure cylinder to said reserve chamber is substantially equal to the ratio between the pressure cylinder arealess theoperating rod area and the operatingrod area,where'bywhen the piston moves toward said valve body the necessary volume of fluid will flow past said piston to keep the portion of the pressure cylinder on the operating rod side of said piston continually filled with fluid, and said pressure responsive means and velocity responsive means also being so related that said pressure responsive means will provide the majority of the con- 'trolof the flow of fluid from the one side of said 'piston to the other side and from the pressure cylinder to the reserve chamber during low piston velocities, and the combination of said piston and Valve -body velocity responsive means will provide the majority of the control of the flow of fluid from the one side of said piston to the 1 other side thereof and from the pressure cylinder to the reserve chamber during relatively high piston velocities.

5. In a hydraulic shock absorber, a pressure cylinder and a reserve chamber, both of which normally contain hydraulic fluid, means closing the opposite ends of said pressure cylinder including a valve body adjacent one end thereof, a piston slidably disposed-in said pressure cylinder, an operating rod connected with said piston and extending through the closure means at the opposite end of said pressure cylinder from said valve body, said piston having a passageway through which iluid may iiow from the valve body side of said piston to the opposite side thereof during the compression stroke of said piston or movement thereof toward said valve body, the area of said piston passage means being not less than .4% nor more than 5 of the area of the pressure cylinder less the area of said operating rod, said valve body having a passageway through which fluid displaced by said operating rod may ilow from said pressure cylinder to said reserve chamber during the compression stroke of said piston, the sizes of the piston passageway and the valve body passageway being of a ratio substantially equal to the ratio between the pressure cylinder rod area, whereby when said piston moves toward said valve body the necessary volume of fluid will iiow through said piston passageway to keep the portion of the pressure cylinder on the operating rod side of said piston continually lled with fluid, and the sizes of said passageways also being such that at high piston velocity said passage- Ways will provide resistance to iluid ilow therethrough which will provide a substantial portion of the total resistance to said piston movement.

6. A hydraulic `shock absorber comprising a pressure cylinder normally filled with liquid, means serving as a liquid reservoir for said pressurecylinder, closure means closing one end of said pressure cylinder, a base valve assembly adjacent the opposite end of said pressure cylinder for controlling the ow of liquid from said pressure cylinder to said reservoir, a piston reciprocable in said pressure cylinder, an operating rod connected with said piston and extending through said closure means; said piston having a passage extending therethrough to permit the ow of liquid from the side of the pressure cylinder adjacent the base valve assembly to the opposite side of said pressure cylinder, said piston passage having an area of not less than .4% nor more than area less the operating rod area and the operating 5% of the area of said pressure cylinder less the area of said operating rod, said valve assembly including a body having a passage extending therethrough to permit a flow of liquid from said pressure cylinder to said reservoir, pressure responsive valve means for controlling the flow of liquid through said base valve body passage, said valvemeans being automatically actuatable to an open position by a predetermined liquid pressure to permit fluid to flow from said pressure cylinder to said reservoir, said base Valve assembly providing resistance to the flow of liquid from said pressure cylinder to saidv reservoir which is [substantially equal to but not less than] ai least as great as the resistance to liquid flow provided by said piston at all operating'piston velocities of the shock absorber.

7. A hydraulic shock absorber comprising va pressure cylinder normally filled with liquid, means serving as a liquid reservoir for said pressure cylinder and closure means closing one end of said pressure cylinder, a valve assembly adjacent the opposite end of said pressure cylinder controlling the flow of liquid from said pressure cylinder to said reservoir, a piston reciprocable in said pressure cylinder, an operating rod connected with said piston and extending through said closure means, said piston having a passage extending therethrough to permit liquid to iiow from the portion of said pressure cylinder between said piston and valve assembly to the portion of said pressure cylinder on the opposite side of said piston, pressure responsive valve means controlling the flow of liquid through said piston passage and being actuatable to open position in response to a predetermined pressure of liquid in said passage, the area of said passage being not less than .4% nor more than 5% of the area of said pressure cylinder less the area of said voperating rod, said valve assembly including a body having a passage extending therethrough to permit a iiow of liquld from said pressure cylinder to said reservoir, pressure responsive Valve means for controlling the flow of liquid through said valve passage and being automatically actuatable to open position in response to a predetermined pressure of liquid in said passage, said valve assembly passage and said valve assembly pressure responsive valve means providing resistance to the flow of liquid from the pressure cylinder to the reservoir which is [substantially equal to but not less than] at least as great as the resistance to liquid flow provided by the piston passage and valve means to the ow of liquid past said piston at all operating piston velocities.

8. A hydraulic shock absorber comprising a pressure cylindernormallyiilled with liquid, means serving as a liquid reservoir for said pressure cylinder, closure means closing one end of said pressure cylinder, a valve assembly adjacent the opposite end of said pressure cylinder for controlling the flow of liquid from the pressure cylinder to the reservoir, a piston reciprocable in said pressure cylinder, an operating rod connected with said piston and extending through said closure means, said piston having passage means extending therethrough to permit liquid to ow from the portion of said `pressure cylinder between said piston and valve assembly to the portion of said pressure cylinder on the opposite side of said piston, the area of said piston passage through, valve disk means normally vengaging one "faceof' said body so as to close one end of said passage against the now of liquid therethrough, means supporting said valve disk means in engagement with said valve body face so that said disk means is automatically actuatable to open position in response to a. predetermined liquid pressure in said valve body passage, said valve assembly providing a greater resistance to the il'ow of liquid therepast than said piston at any given operating piston velocity.

9. A hydraulic shock absorber including a pressure cylinder normally filled with liquid, means serving as a liquid reservoir for said pressure cylinder, closure means closing one end of said pressure cylinder, a valve body adjacent the opposite end of said pressure cylinder'permitting the ow of liquid from said pressurecylinder to said reservoir, a piston reciprocable in said pressure cylinder, an operating rod connected with said piston Aand extending through said closure means, said piston having passage meansY extending therethrough to permita flow of liquid from the portion of said pressure cylinder between said piston and said valve body to the portion of said pressure cylinder on the opposite side of said piston during movement of said piston toward said valve body, said valve body having a passage therethrough through which liquid displaced by said operating rod may ilow from said pressure cylinder to said reservoir during the compression stroke of said piston, said valve body passage having a flow capacity allowing a relatively free flow of liquid therethrough at low piston velocities, pressure responsive valve means for controlling the flow of liquid through said valve body passage, said valve means being automatically actuatable to open position in response to a predetermined pressure of liquid in said valve body passage, the ratio of the sizes of the piston compression passage and base valve compression passage being substantially equal to but not less than the ratio between the pressure cylinder area minus the operating rod area and the operating rod area, whereby when said piston moves toward said base valve body the necessary volume of liquid will flow through. said piston compression passage to keep the portion of the pressure cylinder on the operating rod side of the piston continually lled with liquid, and the area of said piston passage means being not less than .4% nor more than of the area of said pressure Ycylinder' less the area of said operating rod.

10. A hydraulic shock absorber, including a pressure cylinder normally filledwith liquid, means serving as a liquid reservoir for said pressure cylinder, closure means closing one end of said pressure cylinder, a valve body adjacent the opposite end of said pressure cylinder permitting a flow of liquid from said pressure cylinder to said reservoir, a p-iston reciprocable in said pressure cylinder, an operating rod connected with said piston and extending through said closure means, said piston having passage means extending therethrough to permit a flow of liquid from the portion of said pressure cylinder between said piston and valve body to the portion of said pressure cylinder on the opposite side of said piston during movement of said piston toward said valve body, pressure responsive valve means normally closing said piston passage against the ilow of liquid therethrough and actuatable to open position in response to a predetermined pressure of liquid in said passage means corresponding to low piston velocity, said valve body having passage vmeans extending therethrough through which liquid displaced by said operating rod may flow from said pressure cylinder to saidreservoir during the compression stroke of said piston, said valve body passage having aflow capacity allowing a relatively free flow of liquid therethrough at low piston velocities, pressure responsive valve means for controlling the now of liquid through said valve body passage means, said valve means being automatically actuatable to open position in response to a predetermined pressure of liquid in said valve body passage means, which predetermined pressure is greater than the predetermined pressure for actuating said piston pressure responsive valve means, the ratio of the sizes of said piston compression passage means and base valve compression passage means being substantially equal to but not less than the ratio between the pressure cylinder area minus the operating lrod area and the operating rodarea, whereby when said piston moves toward said base valve body the necessary volume of liquid will flow through said piston compression passage -means to keep the portion of the pressure cylinder on the operating rod side of the piston continually lled with liquid, and the area of saidpiston passage means being not less than .4% nor more than 5% of the area of said pressure cylinder less the area of said operating rod.

11. A hydraulic shock absorber comprising a pressure cylinder normally lled with liquid, means serving as a liquid reservoir for said pressure cylinder, closure means closing one end of said pressure cylinder, a base valve assembly adjacent the opposite end of said pressure cylinder for controlling the flow of liquid from said pressure cylinder .to said reservoir, a piston reciprocable in said pressure cylinder, an operating rod connected with said piston and extending through said closure means, said piston having a passage extending therethrough to permit the flow of liquid from the side of said pressure cylinder adjacent the base valve assembly to the opposite side of said pressure cylinder, said piston passage having an area of not less than .4% nor more than 5% oi the area of said pressure cylinder less the area of said operating rod, said valve assembly including a body having a passage of predetermined size extending therethrough to permit a flow of liquid from said pressure cylinder to said reservoir, said passage size being such as to permit a relatively free flow of huid therethrough at all operating piston velocities, pressure responsive valve means for controlling the flow of liquid through said base valve body passage, said valve means being automatically actuatable to an open position by a predetermined liquid pressure to permit liquid to flow from said pressure cylinder to said reservoir, said base valve assembly providing resistance to the flow of liquid from said pressure cylinder to said reservoir which is [substantially equal to but not less than] at least as great as the resistance to liquid flow provided by said piston at al1 operating piston velocities of the shock absorber.

l2. A hydraulic shock absorber as deilned in claim 3, in which the pressure cylinder area, less the operating rod area is substantially in the ratio of three to one to the operating rod area, and the ratio of the flow capacity of the piston compression passageway means to the ilow capacity of the base valve compression passageway means also being substantially three to one.

13. A hydraulic shock absorber comprising a. pressure cylinder normally lled with liquid,

vmeans serving as a liquid reservoir for said prescent the opposite end of said pressure cylinder controlling the flow of liquid from said pressure cylinder to said reservoir, a piston reciprocable in said pressure cylinder, an operating rod connected with said piston and extending through said closure means, said piston having a passage extending therethrough to permit liquid to` flow from the portion of said pressure cylinder be- 1tween said piston and valve assembly to the portion of said pressure cylinder on the opposite side of said piston, pressure responsive valve means controlling the flow of liquid through said piston passage and being actuatable to open position in response to a predetermined pressure of liquid in said passage, the area of said passage being substantially 2.3% of the area of said pressure cylinder less the area of saidoperating rod, said valve assembly including a body having a passage extending therethrough to permit a iiow of liquid from said pressure cylinder to said reservoir,

is [substantially equal to but not less than] at least as great as the resistance to liquid flow provided by the piston passage and valve means to the ow of liquid past said piston at all operating piston velocities.

RALPH H. WHISLER, Jn.

REFERENCES CITED The following references are of record in the lle of the patent or the original patent:

UNITED STATES PATENTS Number Name Date 2,107,974 Bechereau et al Feb. 8, 1938 2,335,907 Boor et al Dec. '7, 1943 

